Methods and devices for controlling an internal combustion engine ascertain the desired torque on the basis of the driver input and convert it into a fuel quantity to be injected. Preferably, a fuel quantity to be injected during an injection cycle is specified in the process. This fuel quantity and the engine torque define the operating point of the engine. From this, additional variables such as air mass setpoint values are calculated. This means that these inputs or family of characteristics must likewise be provided for different operating modes.
The fuel quantity resulting in this conversion exclusively relates to a specific operating mode of the engine. In one operating mode, in a diesel engine, for instance, this is lean-combustion operation with conventional diesel combustion, or the regeneration operation for scavenging a particle filter. The operating modes differ considerably in their efficiency and thus in the fuel quantity to be injected in the same operating point. This worsening of the efficiency is attributable to the fact that in the regeneration fuel is injected in an angular range that renders only a negligible or no contribution to the overall torque. In order to achieve the desired torque, the fuel quantity may therefore have to be corrected. As a result, the conversion of torque into fuel quantity can no longer be used for the unambiguous definition of the engine operating point.
This means that for each operating mode a different calculation rule or different parameters must be used to calculate the fuel quantity on the basis of the torque. This considerably complicates the application of the variables as a function of the operating point.
Since the variables as a function of the operating point differ between different operating modes, a transition function must ensure the continuous transition during the switchover between the operating modes. The variables to be switched are usually ramped to the new value. The same applies to the fuel quantity. Since the fuel quantity reference variable and the setpoint values are ramped simultaneously, the profile of the setpoint values during the switchover is unpredictable. Consequently, the application of the operating mode transitions is not possible.